I was just checking out the online price list for the Golf and found something interesting on page 13.
On the Enviromental Info page theres a section for cars built upto 5.11.06 and then cars built from 6.11.06.
If you look at the GTI, the emissions have dropped on the newer built cars, but the output has stayed the same. Looks like the "claimed" MPG has very slightly improved too.
VW have obviously been tweaking.
At the bottom of the page it says "Effective from 1 January 2007".